Nodular hepatocellular carcinoma: variation of tumor conspicuity on single-level dynamic scan and optimization of fixed delay times for two-phase helical CT.

PURPOSE The purpose of this work was to determine the optimal delay times in two-phase helical CT for nodular hepatocellular carcinoma (HCC). METHOD Twenty-four patients with nodular HCC (size 2.1-6.7 cm, mean 4.2 cm) were divided into three groups to undergo single-level dynamic CT with 150 ml of contrast material (iodine load of 45 g) at a rate of 3 ml/s. CT acquisition started 10, 30, or 60 s after the injection for each group, respectively, and lasted for 110 or 120 s. The optimal 20 s windows that allowed a tumor-to-liver contrast of >10 HU were determined in the pooled tumor-to-liver contrast curve. RESULTS The determined temporal windows were 36-56 and 130-150 s, respectively. However, each window was not appropriate in seven (33%) and five (36%) patients because of the individual variations of the contrast curve. CONCLUSION There is no optimal fixed delay time that is appropriate in all individual patients. The best delay times are 36 and at least 130 s with our injection protocol.